Matt here. Have a 98' GMC Sierra 350/NV3500 with original black box PCM 16250279. Have owned EFILive Flashscan V2 for a decade and a half. Originally purchased to tune fuel gauge level reading and adjust tire size calibration for larger tires in the past. Didn't do much tuning experimentation until purchasing a travel trailer 4 years ago and started chasing more consistent DFCO activation and getting rid of knock. Was able to sort of get the AutoVE tuning thing to work using the stock O2's and tweaked the main timing table until I was happy with the trucks performance towing the camper.

Didn't do much else tuning wise for a few years. About 1.5 years ago I got a motivated to solve the "buzzing" or "hummingbird" fuel gauge needle. EFILive never offered anything for the 98-00 Vortec PCM's regarding fuel system other than allowing to change the programmed tank volume (gallons). The guys on the (now defunct) PPE forum went down the rabbit hole with passive components (resistors/capacitors) and having to then rescale the gauge range (using HPtuners or others), but this never made sense to me. Instead I first borrowed a scope to understand what frequency the PCM drove the gauge at. Was basically able to figure out a PWM frequency of 59Hz from the PCM.
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Then decided this would be a good opportunity to get into the Arduino scene and try to use an Attiny85 or Trinket or other to sample the fuel gauge PWM duty from the PCM and then drive the gauge directly with the Arduino at a much higher frequency. Scratched a lot of notes out, broke into the circuit from the gauge to the PCM pin (green wire under/around the brake booster/clutch master), grabbed a spare cluster from the yard to experiment with, and finally got something to work. I think I had the Arduino driving the gauge at around 32Khz or something crazy, but it was rock solid.
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I then fell down the rabbit hole of trying to get a board prototyped that would include all the needed components that I could solder thru hole style myself. This was in the winter, and my next step was to actually purchase the board and figure out how/where to integrate it to the dash wiring harness. I had the thought to wire it into the convenience center box, but would need to pull the dash and its harness to do the job correctly. Camping season started and I lost interest again.
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Happened to be browsing a GMT400 specific truck forum and saw a guy posting about being able to eliminate the typical fuel gauge buzz using JETDST. I had never considered the JET product, since it wasn't TunerCAT any longer (should have purchase software a decade ago) and I figured it couldn't do anything that EFILive couldn't already do. Apparently I was wrong, as he posted screenshots of being able to change the fuel gauge PWM frequency, and the stock setting is apparently 59Hz. This exactly matched the frequency I discovered myself with the scope. I quickly found someone selling the 14005 USB version with a single license left over, and grabbed it used.

I haven't done too much with JET yet, but have confirmed it can adjust the fuel gauge PWM frequency. Also interesting, is that a license is not used to read a PCM to .jcl file. I had read many times that a license is used just reading a PCM. This is not my experience. I also learned, when reading about the JET software, that it could save as BIN file format. This was very interesting to me, as I'd love to educate myself enough to be able to figure out exactly what parts of the BIN file are being modified when the gauge PWM frequency is changed, in order to ultimately learn how to write CAX files for EFILive. I've got an irrational desire to continue to try and make developments for the 98-00 Vortec PCM's on EFILive. Everyone else seems to have given up and always recommends swapping to the 411 PCM. I don't need to do this, but I'd welcome the challenge to open up more functionality on the black box PCM.

Anyway, very long intro, and now I am off to post in the OBDII tuning forum to see if anyone knows why I can't seem to get a good BIN file saved from JET. Or if anyone has other suggestions for pulling BIN files from Vortec black box PCMs, thru the OBDII port.